Sydney co-captain Kieren Jack is set to be sidelined for the next three weeks after the club confirmed he injured the medial ligament in his left knee in Saturday night’s win over the Suns.

“It is a really disappointing setback for Kieren and as our co-captain, he is clearly an important player for us,” Sydney general manager of football Tom Harley said on Sunday.

“He is the ultimate professional and will work closely with our medical staff to do everything he can to get himself right.”

Jack could still feature in the finals if the Swans can make it to the Grand Final.